The present invention relates generally to detection and recording of high intensity electrical currents and more particularly to detection and recording of lightning currents flowing in a lightning conductor for instance in a wind turbine.
In order to guarantee adequate maintenance of systems which could potentially be subjected to unwanted high intensity electric currents flowing through the system, for instance if the system forms part of the lightning current path in a lightning conductor, it is often required continuously to monitor the system and to measure and record the intensity of lightning currents, the date of the lightning current and the number of the occurrences of lightning currents within a given period of time.
A method and an apparatus for measuring and recording a lightning current in a lightning conductor is disclosed in EP757797 (xe2x80x9cMethod for monitoring lightning protection equipmentxe2x80x9d). This apparatus basically comprises a magnetic core around the lightning conductor such that a lightning current flowing in the lightning conductor will generate a magnetic field in the core. A winding is disposed around said core such that said magnetic field by means of induction will generate an electric current in the winding. The winding is coupled to a measuring circuit and a recording circuit which records the intensity of the lightning current and the date of the lightning current. These circuits are powered by means of a power supply. Furthermore the recorded data can be forwarded to a telephone line via a non-galvanic coupling (for security reasons).
U.S. Pat. No. 5,892,430 furthermore discloses a self-powered powerline sensor comprising a core layer for wrapping about an AC powerline, a winding layer comprising a number of windings to be energised by the AC current flowing in the powerline and disposed about the core layer, means for sensing relevant conditions in said AC powerline and means powered by said windings and in communication with said sensing means for transmitting a signal representing said conditions in the AC powerline.
Furthermore U.S. Pat. No. 4,904,996 discloses a mobile monitoring system for moving on a conductor of an AC powerline and comprising front and rear propulsion modules surrounding said conductor and used to carry the monitoring equipment between them. This equipment comprises means such as video and infrared cameras and means for detecting problems and dysfunctions on the powerline. The equipment also comprises transmitter means for communication with a ground receiver.
Finally JP 8227788 A discloses a lightning surge measurement system for use in high voltage transmission installations comprising a detection coil the signals from which are converted into optical signals and transmitted to a ground station through a optical fibre.
In order to guarantee un-interrupted operation of a monitoring system for lightning protectors it is important that the power supply which supply monitoring circuits with electric energy should be protected against failure for instance caused by a power line drop-out, a failure which might remain unnoticed for a period of time. One method of circumventing such problems is to provide the system with some kind of power supply backup means, but a more advantageous solution would be to be able to avoid a power line driven power supply altogether. The present invention addresses this possibility.
It is the object of the present invention to provide a detector for high intensity electric currents such as lightning currents in a lightning conductor for instance in a wind turbine, said detector continuously monitoring lightning currents in the lightning conductor where said detector provides improved reliability, in that the power needed by the detector means is provided by the lightning current itself instead of by a power supply coupled to the mains supply. This object is achieved with the aid of a system comprising the features set forth in the charactersing clause of claim 1. One specific embodiment hereof is defined in claim 2.
It is a further object of the present invention to provide a safe and reliable transmission of data from said detector to succeeding recording and/or processing equipment located at a remote position relative to the detector. This object is achieved according to the features set forth in the characterising clause of claim 3.
Further advantageous embodiments of the invention are described in the remaining of the independent claims.
The advantageous effect of the present invention is that the operation of the detector is independent of external power supply, so that its operation remains unaffected by for instance dropouts of mains voltage. Such dropouts are typical in connection with lightning activity and in some places mains supply is even deliberately shut-down during lightning activity. Dropouts of mains supply during lightning activity is thus a typical situation.